Chronotropic incompetence (CI), broadly speaking, is the inability of the heart to increase its heart rate commensurate with increased activity or demand. CI is a problem that affects patients suffering from a variety of different cardiovascular diseases. For example, CI can affect approximately a third or more of heart-failure patients. CI can affect an even larger percentage of patients that have a pacemaker.
When an individual has a chronotropically competent heart rate response (e.g., the individual does not have CI), cardiac output is increased in response to exertion to meet the increased metabolic demands of the body. When an individual has CI, cardiac output is limited and unable to meet the increased metabolic demands of the body from exertion. CI can limit the amount of activity, whether exercise or daily tasks, a person can undertake without feeling tired. As such, CI can significantly limit the quality of one's life. CI is also correlated with cardiovascular mortality.